We continue to study placental proteins as cancer markers. In patients with primary hyperparathyroidism, determination of the subunits of human chorionic gonadotropin may help make the diagnosis of parathyroid carcinoma or screen for associated malignant pancreatic islet disease. The subunits of CG appear to be nonspecific but particularly sensitive markers for malignant transformations of gastrinomas. Immunocytochemical demonstration of placental lactogen supports the placental origin of the syncytial giant cells in so-called "syncytial endometritis". Placental cells transformed by temperature-sensitive mutants of SV40 virus produce low levels of pregnancy-specific beta1-glycoprotein (SP1) at the permissive temperature (33C), but at the restrictive temperature (40C) where the transformed phenotype was lost, SP1 production was greatly enhanced. SP1 exists in solution in the form of aggregates (at least as high as the trimer) that dissociate only slowly on dilution. Purified CG-alpha of urinary origin is heterogeneous and contains forms with terminal N-acetylglucosamine.